1. Field of the Invention
The present invention relates to a real-time temperature measuring, and more particularly, to an apparatus for real-time temperature measuring by using the ultrasound system.
2. Description of the Prior Art
In the clinical therapy at recent years, the High-intensity focused ultrasound thermal (HIFU) therapy has already been paid highly attention, wherein the thermal therapy is a kind of non-invasive therapy way which is used in the control of cancer cell and tissue burn etc. Thus the non-invasive therapy has become the biggest feature of ultrasound therapy, and it is unable to be replaced in the medical treatment.
During HIFU treatments, temperature monitoring for treatment guidance is essential for control and treatment optimization. Among the medical imaging modalities, magnetic resonance imaging (MRI) has been proven to precisely detect temperature changes during a treatment due to the effect of temperature-dependent proton resonance frequency shifts.
In the thermal therapy process, in order to control the degree of heating to avoid injuring the normal cell tissue of the surrounding area, the real-time temperature measuring system having the instantaneous regional temperature change is very important. If there is no such kind of monitoring heating system, the clinical doctor is unable to grasp the detailed temperature change accurately in the body. Not only the difficulty of therapy and the danger of operation will be increased, but also the clinical application of thermal therapy will be restricted greatly.
However, in order to use MRI for temperature monitoring, the HIFU system must be designed to be magnetic-resonance compatible, which largely increases the complexity of the system design and increases the cost for its use in clinical applications. Another potential approach to provide sufficient temperature sensitivity and yield good spatial resolution for medical imaging is diagnostic ultrasound. A very basic concept is that the backscattered ultrasound RF echo from the region experiences time shifts after the tissue is heated, which has been identified to be a gross effect including the change in the sound speed and thermal expansion of the tissue in the heated region due to temperature changes. An attractive feature of using diagnostic ultrasound to monitor temperature during HIFU treatments is that this technique is relatively less expensive, portable, and can be easily employed in almost any current HIFU systems with little concern about system compatibility.
Among the ultrasound-based temperature estimation techniques, both frequency-domain-and time-domain-based processing schemes have been proposed. In the prior art, a spectral processing technique was used. The temperature change estimation along one dimension was achieved by tracking the frequency variation in the echo components in the spectral domain; the echo spectrum was estimated using an autoregressive (AR) model. However, the difficulty in implementing this algorithm involves the selection of the order of the AR model and the necessity to have two or more scattering centers per window. As compared to spectral-based processing schemes, a major advantage of time-domain processing is computational efficiency. Moreno et al. and Simon et al proposed that time-domain signal processing schemes are feasible for temperature estimation, where these techniques are conceptually identical to blood flow estimation using pulsed Doppler system.
By using classical quadrature demodulation, the phase differences in successive echoes from moving targets are detected, and the phase change in the signal can be estimated and accumulated; resultantly, the temperature information can be extracted. Although there is an improvement in the computational efficiency, the computation of cross-correlation still involves extensive processing, hindering the progress of the real-time implementation of temperature estimation.
At present, the relevant measuring known in the prior art include the human resistant temperature measuring method, magnetic resonance imaging measuring method, infrared temperature measuring method and ultrasound tissue temperature measuring method etc. These techniques can be used to monitor the tissue temperature, but each technique has its own shortcomings. For example, the shortcomings of the human resistant temperature measuring method are poor space resolution and higher variation, and it is seldom used in the clinical application. Though the magnetic resonance imaging measuring method can provide higher space resolution, but the real-time measurement is unable to be achieved due to slower scanning speed. Moreover, the procurement cost of equipments will be very high and the volume space of system will be quite huge, and it is not easy to be integrated with other thermal therapy methods, thus it is not practical in the clinical thermal therapy. The infrared temperature measuring method is unable to provide the temperature change of deep tissue, thus it is not suitable to be used as the monitoring equipment of temperature change in the thermal therapy process.
However, the insufficient information for the inside temperature of tissue become the greatest restriction in the process. Though the traditional ultrasound technique can be used to obtain temperature distribution information, but the operating time is too long, and the real-time information is unable to be obtained, thus it is not suitable for the clinical therapy.
Quite clinically, the application of ultrasound as the tool for diagnosing the disease has already been used widely, and its safety has been trusted. The main advantages are the followings: non-invasive measurement, real-time image scanning, strong system mobility, and cheap system cost etc. Thus, if the ultrasound system can be utilized to develop non-invasive temperature monitoring system for the tissue, and can be combined other medical systems such as the ultrasound imaging system, the application range of clinical thermal therapy and relevant medical safety will be able to be increased greatly.